The present invention relates generally to the field of musical instruments. In particular, the present invention involves an improved musical instrument having a frame or body that is lightweight and compact. Additionally, in some embodiments, the instrument can be designed to offer unique resonance characteristics.
Musical instruments are formed having a means for producing a vibration of a fluid or magnetic field surrounding the instrument, the fluid most often being air. The vibration, when received by the human ear, is interpreted as an audible sound. In order to produce enough sound to be useful to a musician, in playing music, the instrument must have a means for harnessing the vibration or must amplify the vibration.
Further, all musical instruments have a sound generating mechanism, that produces one or typically a plurality of vibrations at a plurality of frequencies, and have a body to which the generating mechanism is attached. The sound created by a sound generating mechanism (e.g. strings, drum heads, and the like) may occasionally be comprised of a single natural frequency, but nearly always, the sound is comprised of several frequencies, with the first, or lowest, natural frequency usually being the dominant one. This lowest, first natural frequency is often referred to as the fundamental frequency. For example, a violin playing concert A pitch generates a sound spectrum comprised of vibrations at many frequencies, but wherein most of the sound energy is concentrated at 440 Hz. This lowest natural frequency is often referred to as the fundamental frequency of concert A.
In stringed instruments, for example, the body of an instrument, such as a guitar, may be hollow in order to amplify the vibrations produced by the strumming or plucking of the strings attached to the instrument. However, in order to provide a large enough cavity to produce the required amount of sound, the body portion of these devices has traditionally had to be large. Typically, one problem with a large body has been the awkwardness of the large shape of the device in use and in storage.
A solid has also traditionally been used to make an instrument body, such as a guitar. This style is comprised of a solid, typically wood, body and one or more electrical pickups used to interpret the vibration of the sound generating mechanism interpreted by the instrument for purposes of amplification. The solid body is used to provide a structure on which to mount the strings and pickups. However, since these devices are constructed of a solid body, they are typically heavy and, therefore, are undesirable for long periods of use.
A common problem with musical instruments is that the body also has its own natural frequencies and will, therefore, begin to resonate as it is affected by the vibrations emanating from the sound generating mechanism. The amplitude and spectrum of these additional body vibrations may be of a benefit to a musician, however, in some situations these vibrations may be unwanted noise or, worse, may interact with the musical tones created by the sound generating mechanism to form dead spots or hot spots within the audible range of the instrument. These body vibrations may also act to distort the audible spectrum of the sound generating mechanism.
The equation generally utilized to identify the natural frequencies of a physical thing includes the components       k    m  
where k=stiffness and m=mass. In this equation, to account for multiple modes of vibration the components k and m may be matrices. The vibrational spectrum of an instrument body is what characterizes its performance. The vibrational spectrum of an instrument body also has a resonance spectrum. Resonance peaks occur as modal natural frequencies or a combination of multiple modal natural frequencies within the vibrational spectrum. The peak resonance of a body is the highest amplitude resonance measured during a resonance test.
Traditionally, it has been believed that the best sound quality could be produced if the mass of the body was high and if the stiffness of the instrument body was also high, because the instrument would be capable of a wide range of tones without a significant amount of unwanted tone produced by the instrument body itself. However, the result of this combination is an instrument body with high mass, and high stiffness that has its set of resonance peaks falling primarily within the range of fundamental frequencies of the played notes of the sound generating mechanism. The range of played notes is called the tonal range.
Most instruments still attempt to achieve the stiffness necessary to form these tones by utilizing traditionally known stiff materials, such as aluminum, wood, or carbon fiber sheets in traditional constructions. For example, a solid bodied guitar, having high stiffness, but also has high mass. However, since the mass is high to accomplish the stiffness, similarly, the instrument body absorbs and attenuates portions of the tonal range and lower harmonics of the sound generating mechanism.
It is theorized that the sound quality of an instrument is improved by minimizing the presence of modal resonance peaks of the body at frequencies within the tonal range of the sound generating mechanism. Modal resonance peaks are a result of the natural frequencies of the instrument body itself and, therefore, changes to the traditionally utilized body construction must be made to accomplish minimization of these peaks.
The present invention includes a musical instrument that is lighter in weight, and utilizes less raw material to construct than traditional instruments. Some embodiments of the present invention also provide unique resonance characteristics over prior instrument designs. Additionally, the present invention includes embodiments of a musical instrument that are constructed utilizing the improved strength and rigidity qualities of space frame technology.
Music can be generated by a wide variety of different musical instruments. One of the ways the ear distinguishes one instrument from another is by the differences in the frequency spectrum generated by those instruments. For example, as stated above, a violin playing concert A pitch generates a note in the tonal range and a sound spectrum with most of the sound energy concentrated at 440 Hz, the fundamental frequency of concert A. Similarly, a piano playing a concert A pitch also generates a note in the tonal range and a sound spectrum with most of the sound energy concentrated at 440 Hz. However, the sounds created by the two instruments can be distinguished even though the same fundamental frequency is being played. This difference is known as timbre.
Several factors allow the ear to differentiate a pitch that has been generated. The tone initiation, sometimes called attack, and the timbre are two primary factors in sound differentiation. The timbre of an instrument is generally considered to be defined by the relative magnitudes of the overtone frequencies generated by the instrument.
For two similar instruments, e.g. two violins, timbre is considered the most important method for determining the sound quality between the instruments. That is to say, the overtones and auditory frequency spectrum generated by a specific instrument become the primary method in differentiating the musical quality of similar instruments.
As outlined above, for many instruments, but primarily for stringed and percussion instruments, the spectrum of resonance frequencies that constitute the sound spectrum of the body, significantly differentiates timbre. For example, for a guitar, with the same gauge and type of strings, tuned the same way, and plucked or played the same way, the difference in musical timbre, or tone, relates directly to the instrument body holding the sound generating mechanism, in this case the strings.
Modes of body vibration and the resonance frequencies in the body vibration spectrum can be modeled by finite element analysis (FEA) or with more accuracy, by testing. A simple but effective test method for instrument body resonance spectrum analysis is the impulse or xe2x80x9ctapxe2x80x9dtest.
In this test, the tapping or striking of a physical body sharply with a stiff striker such as a small hammer or metal bar will cause the body to resonate. Assuming the instrument body has been physically isolated from its surroundings, when tapped, it will resonate at all of its resonance frequencies within its range to generate its sound spectrum.
By using a vibration (sound) sensing device such as a low mass accelerometer attached directly to the body, or by measuring the air movement emanating from the body in free oscillations after it is struck, the resonance spectrum can be recorded and analyzed. By providing the time based resonance spectrum data to an instrument such as a spectrum analyzer and/or by performing a Fourier transform on the data, the data can be converted to frequency based information. This information shows the resonance spectrum of the instrument body, i.e. the frequencies that the instrument body enhances or amplifies, and those that it attenuates. This analysis allows timbres of different instruments to be compared.
For a tap or impulse test on a solid body, the contact of the body with the air is considered to have negligible effect on the resonance frequencies spectrum of the body. However, the body should be isolated from other physical structures. For example, allowing the body to be suspended under its own weight from a light string acts to isolate the body from the physical bodies around it, while having only negligible effects on the body resonance spectrum.
Additionally, in order to gather a complete spectrum for analysis, it is best to tap the body at many diverse locations on the surface of the body. The monitoring device or devices can be located at several locations around the instrument, or at a central location, so that the device captures resonance spectrum information in a balanced way.
The natural frequencies of the body are constrained by the physical limitations of the modulus of elasticity, the shape, and the density of the materials utilized. For example, typical guitar bodies"" lowest natural frequencies and peak resonances are in the 30-500 Hz range. It should be noted that these are calculated only with respect to the instrument body itself and not the resonance of the body of air enclosed by the instrument.
Further, by the laws of physics, (see FIG. 7) a music-generating mechanism vibrating at frequencies less than 1.4 times the natural frequency of the specific vibrational mode of the instrument body will be supported or amplified by that mode. Similarly, for generated frequencies greater than 1.4 times the natural frequency of that mode, the instrument body will attenuate or absorb the sound energy of those frequencies. Based upon this principle, a musical instrument body having its modal natural frequencies primarily above the fundamental frequencies typically generated by the sound generating mechanism allows for the support and amplification of those fundamental frequencies and of a wide range of generated musical overtones without absorption and attenuation by the instrument body.
The body of an instrument constructed according to the present invention may have any design that has the described tonal characteristics. For example, a space frame design provides the desired tonal characteristics and also offers excellent stiffness-to-weight and compact design advantages over prior instrument designs.
Space frame technology has long been known and utilized in the field of building construction to improve the strength and rigidity of buildings while reducing the amount of raw materials needed to provide such strength and rigidity. These advantages have been accomplished by the use of simple structural elements and the organization of those elements into orderly geometric polygonal structures. A number of structures may then be connected together, with each structure providing strength to the others, thereby creating a space frame. U.S. Pat. No. 2,986,241, to Richard Buckminster Fuller (hereafter, Fuller), provides good background information regarding the known benefits of strut-type and sheet-type space frame technology, both of which are suitable for application in the present invention, and its subject matter is, therefore, incorporated herein by reference. Any suitable structure providing a space frame design may be utilized. For example, suitable types of space frames include, but are not limited to: strut-type frames, sheet-type frames, and combinations of the two types.
A space frame as applied within this document is a portion of an instrument body shape that has been segmented into a plurality of polyhedral shapes, each having a plurality of faces or sides, with adjacent shapes being in a face to face relationship. Each shape defines a space therein, by a plurality of load bearing members, such as struts, sheets, and the like. It should be noted that the body may be comprised of a plurality of space frames interstitially arranged with respect to each other.
Space frame principles, as applied to building construction, have shown increased structural rigidity and strength with a reduction in raw materials, weight, and space. However, these principles have not been applied to musical instruments. Further the resonance characteristics of a device constructed according to these principles have not been investigated. The resonance characteristics of these style devices are harnessed in embodiments of the present invention.
For example, in one embodiment of the present invention, a stringed musical instrument is comprised of a body constructed from spars in which the spars are arranged utilizing space frame principles. A mechanism for generating a musical tone, such as a vibratory string, set of strings, or drum head, for example, is tensioned across at least a portion of the body. In the stringed embodiment, the tension of the strings is preferably adjustable and the strings should be removable, allowing for their replacement. The body also may have one or more pickups mounted thereto for amplifying the resonance of the string or strings. The body may also have an amplifying unit mounted thereto to aid in amplification, such as an electric pickup. In the stringed embodiment, a fret board may be applied between the space frame and the strings. However, for applications such as for steel-style guitar playing, the device may be utilized without a fret board.
Preferably the instrument, regardless of what style space frame is utilized, has a mechanism for generating a musical tone and a body attached to the mechanism. The body preferably has a peak resonance frequency of at least 1,100 Hz.
The aforementioned benefits and other benefits including specific features of the invention will become clear from the following description by reference to the accompanying drawings.